Quantum Criticality in a Strongly Coupled S=1 Spin Chain System at Ambient Field and Pressure

We report spontaneous appearance of antiferromagnetic order in a model gapped quantum paramagnet Ni(Cl_1-xBr_x)₂-4SC(NH₂)₂ induced by a change in bromine concentration x. The linear soft-mode spin waves, as well as magnetic Bragg peaks are observed directly in a Br-rich material [1]. Comparison with the preceding studies on specimen with lower bromine concentration [2,3] allows us to reconstruct the overall phase diagram. The transition is qualitatively similar to a z=1 magnetic quantum critical point. However, the observed critical scaling of thermodynamic and magnetic properties has rather unusual critical exponents.

[1] K. Yu. Povarov, A. Mannig et al., Phys. Rev. B 96, 140414R (2017)
[2] K. Yu. Povarov, E. Wulf et al., Phys. Rev. B 92, 024429 (2015)
[3] E. Wulf, D. Hüvonen et al., Phys. Rev. B 88, 174418 (2013)